1. Field of the Invention
The present invention relates to an engine braking system which makes an output shaft of an engine perform braking work against itself.
2. Background Art
In general, a large bus or a truck in which the heat-exchange upon friction braking is large, is equipped with an auxiliary braking device in addition to a main braking device. In conventional braking devices, the engine or a rotative resistor is driven by wheels of the vehicle so as to produce resistance loss which serves as a braking force.
Among such known braking arrangements, there are; those which include and use rotative resistors, fluid retarders and electric retarders. An example of a conventional engine braking system is shown in FIG. 9.
As shown in FIG. 9, the fluid retarder 201 is disposed within a driving force transmitting shaft 204 that connects the engine 202 to the wheels 203 of the vehicle, and an eddy is generated in fluid (for example, water or oil) between a rotor 205 fixed to the output side and a stator 206 fixed to the input side so that energy absorbed therein is transformed into heat. The fluid is cooled by a heat-exchanger 208 disposed in a fluid tank 207, and recirculated. Braking effort is adjusted by changing the flow rate by means of a valve 209.
On the other hand, the electric retarder disperses in the form of ohmic heat the eddy current (Foucault current) generated when a rotor of the same kind as said fluid retarder rotates in a magnetic field between electromagnets.
In the above retarders, the output torque is finally changed to heat energy and the thusly transformed energy represents the braking energy. Thus, in order to raise braking efficiency, a device for cooling the working medium is necessary. Disposition of such a device is troublesome in terms of spacing and cost.